1. Field of the Invention
The present invention relates to an image forming device for forming images on a printing medium.
2. Description of Related Art
As disclosed in Japanese patent-application publication (kokai) No. 2000-278543, a process called calibration is conventionally performed to match density of images printed by a printer to tones (density) in print data received from an application program. The calibration process produces correction data through a process described below.
Assuming a full color printer capable of printing 256 levels of each color in a CMYK process using cyan (C), magenta (M), yellow (Y), and black (K) ink, calibration patches (measurement patches) are printed as shown in FIG. 12.
The calibration patches are printed in four rows corresponding to the four colors CMYK, and nine patches (patterns of any desired shape each printed at a uniform color density, referred to as simply “patches” below) are printed in each row. The nine patches in each row are printed by sending nine values representing tone levels 0, 32, 64, 96, 128, 160, 192, 224, and 255, that is, at increments of 31 or 32 levels.
The density of each patch is then measured with a sensor and the measured density is used as the output level. Data indicating correlation between the output levels and the tone or gradation values (input levels) sent to the printer is generated, and correction data for matching, to the measured output levels, the input levels sent to the printer is generated. For each of the nine cyan patches that were printed, for example, correction value required to acquire the ideal output level is obtained by using the actual output level acquired for each of the nine input levels. The correction data for the 247 input levels other than the nine measured input levels is interpolated from the calculated correction values using an interpolation algorithm. In this way, correction values for all input levels 0 to 255 are calculated, and all correction values are saved as the calibration data in a data file.
In subsequent printing operations, the calibration data is read from the data file, tone data contained in the print data received from the application program is converted to tone levels to be sent to the printer based on the read calibration data, and the converted tone data is then sent to the printer. Thus, the color density of the actual printer output matches the density levels (tones) contained in the print data received from the application program.